The build-up of misfolded and/or unfolded proteins in the endoplasmic reticulum (ER) is characterized as the unfolded protein response (UPR). The pathological consequence of this response is known as endoplasmic reticulum (ER) stress and has recently emerged as a possible mechanism for the initiation and progression of numerous disease states, including the alcoholic liver. The ER-resident molecular chaperone, protein disulfide isomerase (PDI), is a key enzyme in both oxidative folding and isomerization reactions. Published data has shown modification of the active-site of PDI by the reactive aldehyde 4-hydroxynonenal (4-HNE). 4-HNE, as well as 4-oxononenal (4-ONE), are products of lipid peroxidation and have been implicated to have a role in the progression of the alcoholic liver. Through the adduction of active site cysteines, these aldehydes have been shown to cause alterations in the enzymatic activity of numerous proteins. The experiments outlined in this proposal are designed to test the general working hypothesis that covalent adduction of PDI by 4-HNE and 4-ONE increase the erred protein burden in the ER and subsequently induces the ER stress response. The first phase of this proposal is designed to elucidate the role of PDI in the ER stress response in vitro, as well as in a chronic ethanol rodent feeding model. Secondly, the alterations in the redox status of PDI will be examined following chronic ethanol feeding. Finally, alterations in the enzymatic activities of PDI will be examined in vivo following ethanol feeding, as well as in vitro, following treatment with the aforementioned aldehydes. Upon completion, the data provided by this proposal will further elucidate the role of PDI in an ethanol-induced ER stress response. With alcoholic liver disease affecting nearly 2 million people in the United States alone, the mechanisms behind its progression remain far from elucidated. The four-year survival rate for end-stage liver disease remains a staggeringly low 35%, stressing an urgency for unraveling the mechanisms behind its pathogenesis. It is most conceivable that the progression of the alcoholic liver is multi-factorial;however, current research suggests a role for both the ER stress response and lipid peroxidation products.